This invention relates to the machining of glass-ceramic materials, and, more particularly, to the laser machining of glass-ceramic radomes.
Glass-ceramic materials are a well-known class of hybrid materials used in a variety of applications. The glass-ceramic materials are strong at elevated temperatures, are hard and erosion resistant, have good thermal shock resistance, and resist crack propagation. They also exhibit good electromagnetic wave transmission properties, which is of particular importance for their use in radomes for missiles and other applications in high-velocity flight vehicles.
Glass-ceramic materials are fabricated into useful articles by first casting the glass-ceramic at elevated temperature into a mold. The cast material, which optionally may be heat treated, is termed a "blank". For many applications, the blank is thereafter machined to remove its surface layers. Where the final article is a radome or other structure that is to be exposed to a high-velocity air flow, the outwardly facing surface must be very smooth and precisely configured.
Generally conical radomes for high-speed applications have been made of glass-ceramic materials for over 30 years. During that period, sophisticated machining techniques have been developed to remove a total of about 0.100 inches from the inside and outside surfaces of the radome blank to produce the precisely configured final article. These machining techniques are based upon material removal by mechanical grinding of the surfaces. In a typical case, grinding is accomplished using a carborundum or diamond grinding wheel to remove about 0.005 inches per pass with a material feed rate that produces about 0.8 cubic centimeters of material removal per minute.
The machining of the glass-ceramic blank by grinding is relatively slow, requires cooling of the workpiece, and is labor intensive. While this approach is operable, there is need to improve process economics by reducing the time and cost to produce glass-ceramic articles such as radomes. The present invention fulfills this need, and further provides related advantages.